ANNUAL REPORT 2011 Tracking changes in the abundance of UK butterflies ANNUAL REPORT 2011 Cover photograph of Orange-tip, Anthocharis cardamines. During a year in which the majority of butterflies emerged early Orange-tip led the way being recorded over three weeks earlier than the average since 1976 whilst also producing its highest index on record. Photograph by Peter Eeles. The text, figures and pictures in this publication are the copyright of the Centre for Ecology & Hydrology and Butterfly Conservation unless otherwise stated and may not be reproduced without permission. This report should be cited as Botham, M.S., Brereton, T.M., Middlebrook, I., Randle, Z. & Roy, D.B. 2013. United Kingdom Butterfly Monitoring Scheme report for 2011. Centre for Ecology & Hydrology. REPORT CONTENTS The UKBMS n About the UKBMS 1 n UKBMS objectives 1 n Contacts 1 BUTTERFLY ABUNDANCE IN 2011 n Survey methods 2 n Summary 2 n Family overview 10 n Species accounts 11 UKBMS NEWS n Online Data Entry for Transect Walker 40 n A new way of analysing UKBMS data 40 FEATURES n The Wider Countryside Butterfly Survey in 2011 41 n Magdalen Hill Down – restoring butterfly populations over the long-term 45 CONTACT DETAILS FOR LOCAL CO-ORDINATORS 49 REFERENCES 51 APPENDICES n Appendix I: Trends in UK BAP status species 52 n Appendix II: Vernacular & scientific names of UK butterfly species 53 ACKNOWLEDGEMENTS (back cover) UKBMS About the UKBMS n To ensure a high level of quality assurance for Welcome to the seventh report of the United butterfly monitoring data by development and Kingdom Butterfly Monitoring Scheme (UKBMS). promotion of standards, and by applying rigorous data validation and verification procedures. Changes in the abundance of butterflies throughout the United Kingdom have been monitored using transects n To secure and manage butterfly monitoring data and since 1976. Over the past 36 years, the huge network of provide access to academia, governments, industry recorders (more than 5,000) has collectively made and the public. almost a quarter of a million weekly visits to almost 2,000 different sites, covering over half a million n To advance knowledge in butterfly ecology through kilometres and counting more than 17 million butterflies. interpretation of butterfly monitoring data. The UKBMS is based on a well-established and n To provide scientific underpinning for solutions to enjoyable recording method and has produced important butterfly conservation issues arising from habitat insights into almost all aspects of butterfly ecology. and climate change. Butterflies are uniquely placed amongst British terrestrial n To provide a knowledge base, including indicators insects and other invertebrate groups to act as indicators of of change, for government policies addressing the state of the environment, allowing us to assess the environmental issues. impacts of habitat change, climate change and the progress of government policy initiatives such as the UK n To promote public awareness and understanding of Post-2010 Biodiversity Framework, National Biodiversity butterflies through communication of the results of Strategies and Action Plans, agri-environment schemes the scheme. and the condition of Sites of Special Scientific Interest (SSSIs). Not only are butterflies biologically suitable as Further information on the UKBMS can be found at indicator species, having rapid lifecycles and, in many www.ukbms.org cases, high sensitivity to environmental conditions, but the recording and monitoring volunteer networks and datasets built up by Butterfly Conservation (BC) and the Contacts Centre for Ecology & Hydrology (CEH) enable accurate assessment of their trends. For general enquiries: Ian Middlebrook, Butterfly Conservation, Manor Yard, The UKBMS is run as a partnership between BC and East Lulworth, Dorset, BH20 5QP. CEH. The scheme also benefits from the active Tel: 01929 400209 involvement of the National Trust (NT), the Royal email: [email protected] Society for the Protection of Birds (RSPB), the Forestry Commission and several wildlife trusts and local For data requests: authorities and is funded by a multi-agency consortium Dr David Roy, CEH, Maclean Building, Benson Lane, (see Acknowledgements on back cover). Crowmarsh Gifford, Wallingford, Oxfordshire, OX10 8BB. Tel 01491 692517 UKBMS Objectives email: [email protected] The UKBMS mission is to assess the status and trends Dr Marc Botham, CEH, Maclean Building, Benson of UK butterfly populations for conservation, research Lane, Crowmarsh Gifford, Wallingford, Oxfordshire, and quality of life. The objectives of the scheme are: OX10 8BB. Tel 01491 692517 n To maintain and develop a network of transect and email: [email protected] other monitored sites in order to assess and interpret changes in the abundance and status of UK Dr Tom Brereton, Butterfly Conservation, Manor Yard, butterflies. East Lulworth, Dorset, BH20 5QP. Tel: 01929 400209 n To encourage participation in scientific butterfly email: [email protected] monitoring by supporting volunteer recording networks. 1 BUTTERFLY ABUNDANCE IN 2011 Survey methods canopy species, Purple, White-letter and Brown Hairstreaks and the Purple Emperor, even though transects In the UKBMS, data on the population status of UK are generally not considered the ideal monitoring method butterflies is derived from a wide-scale programme of for them. However, they are included because ‘extreme’ site-based monitoring. The majority of sites are high or low years in the abundance of these species can be monitored by butterfly transects (Pollard & Yates 1993). determined from transect monitoring and because there The transect method, which was established in 1976, are a small number of transects and timed counts directed involves weekly butterfly counts along fixed routes specifically towards some of these species. through the season made under strict weather, recording area and time of day criteria. Weekly counts for each The Collated Index for each species is updated each year species are summed to generate annual abundance with the inclusion of additional monitoring data and indices. For sites with missing weekly counts, a therefore indices may differ to those presented in earlier statistical model (a Generalised Additive Model, reports. Similarly, the rank order used to show those years ‘GAM’) is used to impute the missing values and to in which butterflies fared better or worse compared to calculate the index (Rothery & Roy 2001). For a number other years, may be modified by these additional data of specialist species (especially the fritillaries) two (see Table 1). As in recent reports, we have produced a ‘reduced effort’ scientific methods, adult timed counts combined single index for all sites for each species rather (Warren et al. 1981) and larval web counts (Lewis & than separate indices for double-brooded species. We are Hurford 1997), are also used to monitor annual currently working on new analytical techniques that will abundance, especially in more remote parts of the UK. In enable us to calculate separate indices for those species both methods, systematic recording is made on single with more than one brood in a year and aim to present days in suitable weather (when UKBMS recording indices for different broods in the future. criteria are met), with the counts converted to a robust index that accounts for both the size of the colony and the time in the season when the count was made. Summary HIGHLIGHTS Data from all past and present transects and timed counts/larval webs at monitored sites are combined each • For a third year in a row more than a thousand sites were monitored with the number of standard transects alone year to derive regional and national ‘Collated’ Indices approaching one thousand. Trends were assessed for 56 (CI) and to estimate trends over time. Because not all of the 59 regularly occurring UK species, which is two sites are monitored each year, a statistical model (log- more than ever before and includes two of our rarer linear regression) is needed to estimate missing values butterflies: Swallowtail and Glanville Fritillary. and to produce indices and trends. The model takes into • 2011 was a record breaking year for butterflies being on account the fact that, for a particular butterfly species, the wing early as a result of the exceptionally warm spring, with 22 species showing their earliest mean some years are better than others (a year effect), typically emergence dates* since monitoring began in 1976. due to the weather, and some sites support larger Several species including Orange-tip and Green populations than others (a site effect). The precision of Hairstreak were on the wing up to three weeks earlier on indices and trends is estimated by a further statistical average than in 2010. A further 10 species recorded their second earliest mean emergence dates*. technique called ‘bootstrapping’. • Spring species had a superb year with Orange-tip having its best year on record and a number of This is now the seventh year that data from a combined threatened species showing large annual increases: UKBMS dataset have been used to calculate trends in Pearl-bordered Fritillary and Duke of Burgundy did butterfly populations. In 2011 the number of UKBMS particularly well with abundance up by more than 50% sites on which butterfly numbers were recorded was more over 2010. than 1,000 for the third year running (966 transects and • After a superb start the season repeated the pattern of 127 larval web/timed counts). Figure 1 shows the UK 2007-2010 and fell away with cool and wet summer weather resulting in the majority of later summer species coverage of these sites in 2011, once again demonstrating having a poor year. As a result, it was a distinctly the immense commitment by volunteers. This enabled average year overall, ranking 18 in the 36–year series. Collated Indices to be calculated for 56 of the 59 regular • A number of species that had a superb year in 2010 species of butterfly in the UK.